In the prior art it is known to obtain an indication of color and brightness characteristics of a paper web during manufacture by an on-line measurement of reflectance value (Rg), but this measurement is decidedly different from that necessary for actual color and brightness characterizations. Accordingly, such a measurement must be accompanied by very frequent off-line testing, so as to enable an adequate empirical calibration of the measuring instrument. Further, a separate set of calibration parameters is required for each grade and weight of paper. Instruments which measure different optical parameters of single sheets sequentially, as by changing from a black backing to a white backing, are not adapted to obtaining two distinct measurements from the same region of a moving web. Laboratory instruments are generally delicate and bulky and not readily adaptable to on-line use.